A printed circuit board is a carrier for electronic components and the metallic conductor tracks which connect them. A large proportion of the demand for base materials for such printed circuit boards is met by glass-fiber-reinforced epoxy-resin boards (FR-4). A continuous increase in the packing density of the electronic components and the automation of the insertion impose qualitatively ever greater requirements on the base material.
In this connection, important criteria are:
(a) High thermal conductivity .lambda. in order to be able to remove the heat produced by the components rapidly; PA1 (b) High surface and volume resistances, low permittivity .epsilon., low loss angle tan.delta., both in a dry and also in a wet atmosphere; PA1 (c) Good thermal and dimensional stability; PA1 (d) Favorable production conditions and good processability; PA1 (e) High chemical stability (towards metallizing chemicals). PA1 (a) .gamma.-methacryloxypropyltrimethoxysilane, vinyltrichlorosilane, methylvinyldichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane and vinyltris(.beta.-methoxyethoxy)silane; owing to the groups Y present in these compounds, these compounds are of importance, in particular, for organically crosslinking (curing) the insulation lacquer; PA1 (b) Diphenyldichlorosilane, diphenyldimethoxysilane and diphenyldiethoxysilane; owing to the groups V present in these compounds, these compounds are used to impart a certain elasticity to the finished coating; PA1 (c) SiCl.sub.4, Si(OCH.sub.3).sub.4, Si(OC.sub.2 H.sub.5).sub.4, Si(n- or i-OC.sub.3 H.sub.7).sub.4 and Si(OC.sub.4 H.sub.9).sub.4 ; such compounds, which result in three-dimensional linkage points in the polycondensation network after hydrolysis, are preferably used to impart a certain hardness (scratch resistance) to the finished coating; PA1 (d) .gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, .gamma.-aminopropylmethyldiethoxysilan e, N-.beta.-aminoethyl-.gamma.-aminopropyltrimethoxysilane and the corresponding N-mono- or N,N-di-methyl- or -ethylsilanes; owing to the radicals Z present in these compounds, these compounds are used particularly in those cases where the polycondensate is to be deposited on the substrate by electrophoretic dip coating.
Substrate materials based on organic polymers are unable to meet entirely the increasing requirements even in conjunction with metal cores (better heat dissipation); thus, for example, FR-4 boards exhibit the following (relatively unsatisfactory) values: .lambda.=0.16 W/m.times.K; Tg=130.degree. C.; .epsilon.=4.5 and tan.delta.=23.times.10.sup.- 3 (at 1 kHz in each case).
As already mentioned above, carrier materials are nowadays required which, inter alia, are able to remove the heat produced by the components rapidly in order to ensure a perfect operation, in particular at high insertion density.
Metallic materials present themselves as ideal heat conductors. Since they are also, in general, excellent electrical conductors, the conductor tracks can be deposited only after the substrate material has been insulated in a suitable manner. Obviously, the insulating coating has to be resistant, particularly in relation to the metallization of the printed circuit board, i.e. it must not be attacked, in particular, by the chemicals which have to be used within the framework of depositing, for example, a copper layer and the later removal of parts of said layer (for example by etching) which are not needed.